Spraying systems are known for creating a high pressure liquid spray and for directing such spray on surfaces or items to be cleaned or treated. Such systems often include a liquid storage tank for holding a supply of the liquid to be sprayed, a pump assembly for pumping the liquid from the liquid storage tank and for increasing the pressure of the liquid to a level which causes the liquid to form a spray, and a spray device connected to the pump assembly for directing the spray in a desired direction. As the liquid storage tank holds a finite supply of the liquid, the level of the liquid in the liquid storage tank will recede during a spraying operation. It is important that the liquid not be completely drained from the liquid storage tank or damage to the pump assembly may result.
Various indicators or alarms can be installed in the spraying system to inform the operator of the level of the liquid in the liquid storage tank or to alert the operator when the liquid level in the liquid storage tank reaches a predetermined low level. For example, liquid storage tanks are often provided with sight gages or transparent windows that allow the liquid level within the liquid storage tank to be visually observed. In addition, it would be possible to have a float activated alarm within the liquid storage tank that would sound an audible bell or illuminate a visible warning light when the liquid level within the liquid storage tank reaches a particular level. Such systems allow the operator to stop the spraying operation before the liquid in the liquid storage tank is completely exhausted.
However, in certain spraying systems, particularly those intended for use outdoors and which may be carried or mounted on a work or utility vehicle, the spray device is usually connected to the pump assembly by an extremely long conduit or hose. When using such a system, it is not unusual for the operator to be located many feet away from the liquid storage tank and pump assembly, both of which remain mounted on the vehicle, when the hose connected to the spray device is at its maximum extension. Thus, the user is not able to see or monitor any sight gages which might be provided on the liquid storage tank, and may not be able to see or hear any alarms or warnings that occur either at the liquid storage tank or the pump assembly. Accordingly, it is still possible for the operator not to know that the liquid level in the liquid storage tank has reached a critically low level when the operator is using the spray device.
Moreover, the known liquid level indicators or alarms described are all relatively complex and add extra cost and expense to the spraying system. For example, liquid storage tanks can be inexpensively molded in one-piece from plastic, but it becomes much more expensive to mold such liquid storage tanks with transparent windows or provide them with external sight gages. Alarms that illuminate lights or sound bells require numerous additional components: a float or other device for sensing the liquid level in the liquid storage tank, an electrical switch which is closed when the float reaches the predetermined low level, a circuit for connecting the switch to a source of electrical energy and to the light or bell, and the light or bell itself. In addition, such alarms require some form of electrical energy for proper operation, and are not extremely reliable, particularly on equipment used outdoors where the components of the alarm are exposed to the weather.